Bio-LPG production process

The present invention is in the field of processes for the production of BioLPG, and catalysts for use in said processes.

Liquefied petroleum gas (LPG) typically comprises propane, butane, or a mixture of the two. LPG may also contain other hydrocarbons in small quantities such as propylene and butylene. At the end of 2018, LPG was estimated to be consumed in an amount of around 300 million tonnes per year. LPG is used in a variety of applications such as fuel for heating appliances, cooking equipment such as outdoor stoves and gas barbeques and certain vehicles.

Historically, LPG has been derived from fossil fuel sources. For example, LPG can be extracted or manufactured during the refining of petroleum or wet natural gas, or extracted from petroleum and natural gas streams as they emerge from the ground. Since conventionally manufactured LPG is a fossil fuel, in order to reduce net carbon emissions, there has recently been increased interest in replacing LPG derived from fossil fuel sources with LPG derived from biological sources (BioLPG). BioLPG (also known as renewable LPG, renewable propane, renewable butane, biopropane or biobutane) has a much lower carbon footprint than conventionally derived LPG. There is thus great interest from the LPG industry and decarbonisation-proponents to expand production volumes of BioLPG.

The following seven general classes of process have been suggested for BioLPG production: i) hydrotreating of bio-oils such as waste vegetable oils; (ii) dehydrogenation of bio-oils and glycerine; iii) fermentation of sugars; iv) hydrolysis and fermentation of cellulosic biomass; v) digestion such as anaerobic digestion by bacteria of wet organic wastes; vi) gaseous conversion and synthesis of cellulosic biomass or organic waste; and vii) liquid conversion and synthesis of cellulosic biomass and organic waste. Many of these processes manufacture BioLPG in low yield as a by-product only, and are principally directed to the manufacture of different products.

Additionally, many of these suggested processes have only been successfully demonstrated in the laboratory or remain at the concept stage, and have not been successfully commercialised. Of the processes discussed above, only hydrotreating of bio-oils has been successfully commercialised. Hydrotreatment is thus the only significant source of BioLPG production. Hydrotreating of bio-oils produces BioLPG as a by-product, and is principally directed to the production of HVO (hydrogenated vegetable oil) biodiesel. In such hydrotreatment processes, the ratio of biodiesel to biopropane produced is typically around 9:1 to 10:1. Some of these hydrotreatment processes involve the hydrotreatment of a purely bio-oil feedstock. However, many processes involve mixing bio-oil with petroleum intermediates to form a blend and hydrotreating the blend to form a mixture of diesel and biodiesel, and a small amount of BioLPG by-product. An in-depth discussion of the various processes known for or suggested for BioLPG production is provided in Process Technologies and Projects for BioLPG, Eric Johnson, Energies, 2019, 12, 250.

There is thus a need for new commercially viable routes for the production of BioLPG. In particular, there is a need for BioLPG production processes that produce BioLPG in high yield.

It is known to use ethanol as a feedstock in various processes for the production of longer chain hydrocarbons such as gasoline and olefins, in which small amounts of LPG are produced as a by-product.

US20140081063 discloses a process for the preparation of high-octane gasoline from bioethanol using a ZSM-5 catalyst. LPG is produced as a by-product of this process in low yields of less than 25%.

Johansson et al., The Hydrocarbon Pool in Ethanol-to-Gasoline over ZSM-5 catalysts, Catalysis Letters, (2009), 127:1-6 discloses a process in which ethanol is converted to gasoline with a ZSM5 catalyst.

Costa et al., Synthesis of Propylene from Ethanol using Phosphorus-modified HZSM-5, Brazilian Journal of Chemical Engineering, Vol. 33, No. 3, pages 503-513 discloses a process for converting ethanol to propylene using a phosphorus-promoted HZSM-5 catalyst. Propane is produced as a minor by-product of the process in yields of less than 10%.

The processes described above are not principally concerned with the production of LPG, but to the production of longer chain hydrocarbons or olefins. LPG is only formed in the processes as a secondary by-product in low yield. The process parameters and catalysts used in these processes are specifically adapted and tailored for the production of olefins and longer chain alkanes.

Thus there is a need for a process in which ethanol can be converted to LPG in high yield, thereby providing a high yield, economically viable LPG production process.

The present invention is based upon the surprising finding that certain aliphatic alcohols can be used as a feedstock in processes for the production of BioLPG in high yield. Using certain process conditions and certain specific zeolite catalysts, aliphatic alcohols such as ethanol or isopropyl alcohol derived from renewable biological sources can be converted to BioLPG in high yield. It has been surprisingly found that catalysts comprising a ZSM5 zeolite material or an MCM22 zeolite material can convert certain aliphatic alcohols to mixtures of biopropane and biobutane (i.e. BioLPG) in high yield under certain reaction conditions. The high yields associated with the present process have not been found to be associated with the use of different zeolite catalyst materials. The particular zeolite materials have also been found to have a longer catalyst lifetime in comparison to other zeolite catalysts when used in the process. An additional advantage of the use of ZSM5 and MCM22 zeolite materials as catalysts is that it has been found that the catalytic activity of these catalysts in the process can be rejuvenated simply after use by exposure to air. Typically, the selectivity and catalytic activity of zeolite catalysts diminishes with the use of the catalyst in a particular process. Whilst it may be possible to rejuvenate the activity of the catalyst to some extent by various methods, it is often not possible to fully rejuvenate the selectivity and activity of a catalyst, meaning that the effectiveness of the catalyst may gradually diminish over time. Surprisingly, it has been found that once diminished through use, the selectivity and catalytic activity of the ZSM5 and MCM22 catalyst materials in the process of the invention can be rejuvenated by exposure to air such that the catalytic activity and selectivity of the catalysts is rejuvenated to a great extent, and in some instances, to the original activity and selectivity of the catalyst in the process. It has additionally been found possible to optimise and tailor the ZSM5 and MCM22 zeolite materials so as to provide novel ZSM5 and MCM22 zeolite catalysts that can be used to provide even higher yields and selectivities for BioLPG in the process, and to have even higher catalyst lifetimes.

According to a first aspect of the invention, there is provided a process for the selective production of BioLPG from C2 or C3 aliphatic alcohols, wherein the process comprises:

Typically, the contacting is carried out at a temperature of from 350° C. to 600° C., and preferably from 375° C. to 500° C.

Typically, the contacting is carried out at a pressure of from 1 atm to 20 atm, preferably from 1 atm to 15 atm, and more preferably from 1 atm to 10 atm.

Alternatively, the contacting is carried out at a pressure of from 3 atm to 50 atm, preferably from 3 atm to 20 atm, more preferably from 3 atm to 15 atm, and most preferably from 3 atm to 10 atm.

Preferably, the contacting is carried out at a temperature of from 350° C. to 600° C. and a pressure of from 3 atm to 10 atm. Most preferably, the contacting is carried out a temperature of from 375° C. to 500° C. and a pressure of from 3 atm to 10 atm.

The process may be carried out as a continuous process. Alternatively, the process may be carried out as a batch process. In preferable embodiments, process steps a) to c) are carried out as a continuous flow process. Preferably, the continuous flow process comprises introducing the feedstream to the reactor vessel at a flow rate of from 1 μL to 10 μL per minute per 150 mg of catalyst present in the reactor vessel; preferably, at a flow rate of from 1 μL to 7.5 μL per minute per 150 mg of catalyst present in the reactor vessel; more preferably, at a flow rate of from 1 μL to 5 μL per minute per 150 mg of catalyst present in the reactor vessel. Most preferably, the continuous flow process comprises introducing the feedstream to the reactor vessel at a flow rate of from 1 μL to 3 μL per minute per 150 mg of catalyst present in the reactor vessel. In some instances, the continuous flow process comprises introducing the feedstream to the reactor vessel at a flow rate of from 1.5 μL to 2.5 μL per minute per 150 mg of catalyst present in the reactor vessel, such as at a flow rate of from 1.75 μL to 2.25 μL per minute per 150 mg of catalyst present in the reactor vessel.

The process may further comprise passing an inert gas through the reaction vessel. Typically, the inert gas is argon. The inert gas is typically introduced into the reaction vessel at a flow rate of from 0.5 ml/min to 10 ml/min per 150 mg of catalyst, preferably from 0.5 ml/min to 5 ml/min per 150 mg of catalyst, more preferably 1.5 ml/min to 5 ml/min per 150 mg of catalyst, and most preferably from 2 ml/min to 5 ml/min per 150 mg of catalyst. In some instances, the inert gas is introduced into the reaction vessel at a flow rate of from 0.5 ml/min to 1.5 ml/min per 150 mg of catalyst, and more preferably from 0.75 ml/min to 1.25 ml/min per 150 mg of catalyst. Preferably, process steps a) to c) are carried out continuously as a continuous flow process and contacting step b) further comprises passing an inert gas through the reaction vessel during contacting step b). Preferably, the inert gas is argon, although other inert gases such as nitrogen may be used.

Preferably, the contacting is carried out at a pressure of from 1 atm to 20 atm; wherein the continuous flow process comprises introducing the feedstream to the reactor vessel at a flow rate of from 1 μL to 3 μL per minute per 150 mg of catalyst present in the reactor vessel; and wherein the process further comprises passing an inert gas such as argon through the reaction vessel during contacting step b), wherein the inert gas is introduced into the reaction vessel at a flow rate of from 0.5 ml/min to 5 ml/min per 150 mg of catalyst.

The process may further comprise contacting the catalyst with an inert diluent gas. Preferably, the inert diluent gas comprises nitrogen. Preferably, process steps a) to c) are carried out continuously as a continuous flow process and contacting step b) further comprises contacting the catalyst with an inert diluent gas such as nitrogen.

Prior to step a), the zeolite material present in the catalyst is preferably present in the H-form. The H-form of a zeolite catalyst is the form in which the zeolite comprises hydrogen cations. Accordingly, prior to step a), if the catalyst is not present in the H-form, the catalyst is treated so as to be present in the form. Accordingly, in some embodiments, the catalyst is contacted with air or oxygen under conditions suitable to provide the catalyst in the H-form. Accordingly, in preferable embodiments, prior to step a), the catalyst is contacted with air or oxygen at a temperature of from 400° C. to 650° C., and preferably from 500° C. to 600° C. More preferably, prior to step a), the catalyst is contacted with air or oxygen at a temperature of from 400° C. to 650° C. for a time period of from 1 hour to 10 hours. Most preferably, prior to step a), the catalyst is contacted with air or oxygen at a temperature of from 4 hours to 6 hours.

In the embodiments described in the paragraph directly above, in some embodiments, prior to step a), but after the catalyst has been contacted with air or oxygen at a temperature of from 400° C. to 650° C. for a time period of from 1 hour to 10 hours, the reaction vessel is heated to a temperature of from 400° C. to 500° C. under air or oxygen flow, preferably, for a time period of from 5 hours to 10 hours, before purging with an inert gas such as argon. Such a step is typically carried out to ensure that the zeolite catalysts are in the H-form.

Preferably, the one or more C2 or C3 aliphatic alcohols comprise ethanol, isopropyl alcohol, or a combination thereof.

In some embodiments one or more C2 or C3 aliphatic alcohols comprise ethanol as the sole C2 or C3 aliphatic alcohol present in the feedstream.

In other embodiments, the one or more C2 or C3 aliphatic alcohols comprise a mixture of ethanol and isopropyl alcohol. For example, in some embodiments, the one or more C2 or C3 aliphatic alcohols comprise ethanol in an amount of from 30% to 70% by weight of the feedstream, and isopropyl alcohol in an amount of from 30% to 70% by weight of the feedstream. In preferable instances, ethanol is present in an amount of from 40% to 60% by weight and isopropyl alcohol is present in an amount of from 40% to 60% by weight of the feedstream. For example, the ethanol and isopropyl alcohol can both be present in the feedstream in an amount of about 50% by weight of the feedstream.

Preferably, the one or more C2 or C3 aliphatic alcohols are derived from renewable biological resources. Thus, in some embodiments, the feedstream does not comprise C2 or C3 aliphatic alcohols derived from fossil fuels. In some embodiments, the feedstream does not comprise any organic compounds derived from fossil fuels.

In preferable embodiments, the one or more C2 or C3 aliphatic alcohols are derived from fermentation or bio-generation.

In some embodiments, the one or more C2 or C3 aliphatic alcohols are produced from fermentation of biological organic material, such as fermentation of cellulosic material. Processes for the fermentation of cellulosic material so as to provide biologically derived C2 or C3 aliphatic alcohols are known in the art.

In other embodiments, the one or more C2 or C3 aliphatic alcohols are derived from recycled carbon. For example, the one or more C2 or C3 aliphatic alcohols may be produced from fermentation of flue gases or bio-generated syngas. Flue gases are the waste product stream of many industrial processes. Flue gases and syngas comprise hydrogen, carbon monoxide and carbon dioxide. These gases can be converted by microorganisms in fermentation processes into C2 or C3 aliphatic alcohols.

The term BioLPG as used herein is to be understood in accordance with the normal meaning of the term in the art. BioLPG is LPG produced from a feedstock that is derived from a biological source instead of fossil fuels. The term derived from a biological source as used herein is used to refer to material that is directly obtained from a biological source or indirectly obtained from a biological source. For example, the term derived from a biological source as used herein encompasses materials obtained by a chemical process where the starting material of the chemical process is obtained from a biological source. For example, where a material obtained from a biological source is chemically processed into a chemical intermediate prior to conversion of the intermediate into LPG, the LPG is still considered to be BioLPG. The term BioLPG as used herein is also used to refer to LPG produced from a feedstock that has been produced by a microbial process such as fermentation. The feedstock for the microbial process such as fermentation may itself have been derived from fossil fuels, for example carbon dioxide or carbon monoxide obtained from the combustion of fossil fuels. LPG produced by such a process is considered to be BioLPG since the feedstock of the LPG production process is a product of a biological process that has a feedstock that is a gas obtained from the combustion of fossil fuels, that would otherwise be released into the atmosphere and contribute to atmospheric carbon levels.

Preferably, the feedstream comprising one or more C2 or C3 aliphatic alcohols comprises the one or more C2 or C3 aliphatic alcohols in an amount of from 70% by weight to 100% by weight, preferably from 80% to 100% by weight of the total weight of components of the feedstream.

In some embodiments, the feedstream comprising one or more C2 or C3 aliphatic alcohols further comprises water. Typically, the water is present in the feedstream in an amount of from 1% by weight to 30% by weight of the total weight of components of the feedstream. Preferably, the water is present in the feedstream in an amount of from 10% by weight to 20% by weight of the total weight of components of the feedstream. In these embodiments, the feedstream typically comprises ethanol in an amount of from 70% by weight to 99% by weight, and preferably from 80% by weight to 90% by weight of the total weight of components of the feedstream.

Surprisingly, it has been found that low levels of water (such as the amounts discussed above) in the process feedstream prolong the lifetime of the zeolite material catalysts. Where the feedstream comprises water, it has been found that the catalyst selectivity and activity for the production of BioLPG remains at a sufficiently high level without deactivation for an increased amount of time compared to where the feedstream does not comprise any water. This is surprising since it is well documented that water vapour at high temperatures often results in dealumination of zeolite catalysts leading to their concomitant deactivation. The extension of catalyst lifetime is particularly advantageous since biologically derived C2 or C3 aliphatic alcohols often comprise water left over from their production processes such as fermentation. Separation of water from biologically derived C2 or C3 aliphatic alcohols so as to provide the anhydrous alcohols is expensive and desirable to avoid if possible. Accordingly, the process of the invention is advantageous in not only does the presence of water in the feedstream not impede the activity of the catalyst, the presence of water in the feedstream actually enhances the lifetime of the catalyst. Where the process is a continuous process, the process can thus be performed continuously for longer periods of time without it being necessary to stop the process intermittently to rejuvenate the catalyst.

The process of the invention has a high selectivity for the production of C3 and/or C4 hydrocarbons over the production of C2 hydrocarbons or longer chain hydrocarbons. BioLPG comprises predominantly C3 and/or C4 hydrocarbons, such as saturated C3 and/or C4 hydrocarbons such as propane and butane.

In some embodiments, at least 90% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products. In some embodiments, at least 95% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products, and most preferably about 100% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products.

In some embodiments, the process of the invention produces C3 and/or C4 hydrocarbons in a yield of at least 20%, at least 30%, at least 40%, at least 50%, or at least 60%. Preferably, the process produces C3 and/or C4 hydrocarbons in a yield of at least 30%.

The exact yield of C3 and/or C4 hydrocarbons will depend upon the nature of the specific process conditions used for a process, and the particular catalyst used in the process.

In some embodiments, the catalyst comprises a ZSM5 zeolite material and the process of the invention produces C3 and/or C4 hydrocarbons in a yield of from 55% to 60%. Preferably, at least 95% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products, and most preferably about 100% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products.

In other embodiments, the catalyst comprises an MCM22 zeolite material and the process of the invention produces C3 and/or C4 hydrocarbons in a yield of from 45% to 55%. Preferably, at least 95% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products, and most preferably about 100% of the one or more C2 or C3 aliphatic alcohols are converted into hydrocarbon products.

In some embodiments, the process has a selectivity for C3 and C4 aliphatic hydrocarbons after two days of at least 30%, when the flow rate of the feedstream is from 1.75 μL to 2.25 μL per minute per 150 mg of catalyst present in the reactor vessel.

The reaction vessel can comprise the catalyst in any suitable configuration or set-up for effectively carrying out the process of the invention. For example, the reaction vessel may comprise a fixed bed reactor. Alternatively, the reaction vessel may comprise a fluidised bed reactor.

Other suitable features of the reaction vessel and means for implementing the process of the invention are those typically used in the art for a catalytic process such as the process of the invention.

In some embodiments, the catalyst comprising the zeolite material may comprise a carrier or support material. However, this is not essential and in some embodiments, the catalyst may be unsupported. Examples of suitable carrier or support materials are those commonly known in the art such as carbon, silica, alumina, or combinations thereof.

In some embodiments, the catalyst comprising the zeolite material may further comprise one or more binder materials. Examples of suitable binder materials include clay or alumina. In some embodiments, the catalyst material comprising the zeolite and the one or more binder materials may be pelleted or extruded. In other embodiments, the catalyst may be free of binder, carrier or support material.

The catalysts comprising zeolite materials for use in the process of the invention may be present as particles of any suitable size for carrying out the process of the invention.

The catalyst comprises a ZSM5 catalyst material, an MCM22 catalyst material, or a combination thereof. As discussed above, the catalysts are preferably present in the H-form of the catalyst. The term H-form of a zeolite as used herein is used in its normal manner in the art to refer to zeolite catalysts in their protonated form.

ZSM5 and MCM22 are zeolite materials known in the art. The terms ZSM5 and MCM22 refer to generic classes of zeolite materials that are defined by a particular structure. Within each class of zeolite materials as used herein (i.e. ZSM5 or MCM22), the silica to alumina ratio (Si/Al ratio) may vary.

Where the catalyst comprises a ZSM5 zeolite material, the ZSM5 zeolite material preferably has a Si/Al ratio of from 20 to 150, more preferably from 25 to 100, and most preferably from 25 to 90. In highly preferable embodiments of the invention where the catalyst comprises a ZSM5 zeolite material, the Si/Al ratio is 30 or 80.